The present invention relates to video tape machines. More particularly, the present invention relates to improved techniques for manufacturing and/or refurbishing a drum assembly that is used in a video tape machine.
Videotape machines that employ drum assemblies including rotating record/reproduce heads are well known. In such machines, a recording medium in the form of tape is wrapped around the drum assembly so that rotating record/reproduce heads can record and reproduce. In general, the heads rotate while the tape is moved (or held stationary) around the drum assembly. The heads may include video heads, audio heads and control track heads and in cases where video editing is needed may also include time code heads, audio confidence playback heads, audio-only erase heads, flying erase heads, etc. The drum assembly generally cooperates with loading mechanisms, reel hubs, tape guides, sensors, erase head, capstans to form a mechanical transport assembly that provides the mechanical interface between the video tape machine electronics and the information recorded on the tape.
Videotape machines can be categorized using several criteria, including tape width (ranging from ¼ in up to 2 in), style (open reel and cassette), scanning method (transverse and helical scan) and recording format (e.g., U-Matic, B, C, Betacam, Digital Betacam, DV, etc.). Most commercially successful videotape machines are based on helical scanning methods. In helical scans, a slow moving tape is helically wrapped 180 degrees around the drum assembly that houses the rotating record/reproduce heads. The tape is positioned at a slight angle to the equatorial plane of the rotating record/reproduce heads. As such, the recorded tracks run diagonally across the tape from one edge to the other. Recorded tracks are parallel to each other but are at an angle to the edge of the tape. There are many recording formats that use helical scanning methods. In the C recording format (analog), the videotape machines use 1 inch oxide tape in open reels. In Digital Betacam recording format (digital), the video tape machines use ½ inch metal tape in cassettes. Digital Betacam is generally preferred over C recording formats because of its digital nature and the fact that it can be used for High Definition.
FIG. 1A illustrates a video tape machine 2 that includes a mechanical transport system 3 that is enclosed by a housing 4. By way of example, the video tape machine may correspond to a Digital Betacam editing recorder such as the DVW, DNW, HDW models manufactured by Sony of Japan. FIG. 1B illustrates the mechanical transport system 3 with a loaded cassette 5. By way of example, the mechanical transport system 3 may correspond to the mechanical transport system used in the DVW-500A model Digital Betacam editing recorder manufactured by Sony of Japan.
As shown in FIG. 1B, the mechanical transport system 3 includes a tape running system 6 having various components 11 including guides, capstan, pinch roller, tape cleaner and the like. The mechanical transport system 3 also includes stationary heads 8 and rotary heads 9 that are disposed in a drum assembly 10. The tape running system 6 is configured to direct a tape 7 around the drum assembly 10 so that the tape 7 engages the rotary heads 9 for recording and reproducing on the tape 7. As shown, the tape running system 6 includes at least an entrance guide 12A for introducing the tape 7 to the drum assembly 10 and an exit guide 12B for removing the tape 7 from the drum assembly 10. As should be appreciated, while the tape 7 is moved around the drum assembly 10 by the tape running system 6, the rotary heads 9 rotate at great speeds reading data from the tape 7 and writing data to the tape 7. Although not shown, the drum assembly is in a tilted position for helical scanning.
Referring to FIGS. 2A & 2B the drum assembly 10 will be described in greater detail. FIG. 2A is a perspective view of the drum assembly 10, and FIG. 2B is a side elevation view, in cross section, of the drum assembly 10. As shown, the drum assembly 10 includes an upper drum 12, an inner drum or scanner 14, a lower drum 16, a drum support 18, a spindle assembly 20, an upper base 22 and a lower base 24. The inner drum 14, which is disposed inside an opening 26 formed in the upper drum 12, is attached to the spindle assembly 20. The inner drum 14, among other things, includes a plurality of record/reproduce heads 9 configured for video recording. The record/reproduce heads 9 are disposed in a gap formed between the upper and lower drums 12 and 16. As should be appreciated, the record/reproduce heads 9 are rotated via the spindle assembly 20 to accomplish any recording or reproducing tasks. The inner drum 14 also includes a cavity 32 for allowing a slip ring assembly (not shown) to be positioned therein. Slip ring assemblies carry electrical signals between the rotating heads and other equipment with which the rotating head has relative motion. By way of example, representative slip ring assemblies may be found in co-pending patent application Ser. No. 09/721,436, which is titled “Slip Ring Assembly For Use In a Video Recorder” and filed on Nov. 22, 2000, and which is herein incorporated by reference.
The lower base 24 is structurally coupled to the upper base 22 and the upper base 22 is structurally coupled to the lower drum 16. The drum support 18 is configured to hold or support the upper drum 12 relative to the lower drum 16. As should be appreciated, the tape moves over the outer peripheral surfaces 12A and 16A of the stationary upper and lower drums 12 and 16 while the rotary heads 9 rotate in order to record or reproduce. The lower drum 16 includes a shoulder 28 for supporting the tape and guiding the tape along the outer peripheral surfaces 12A and 16A of the upper and lower drums 12 and 16 adjacent the rotary recording/reproducing heads 9. As shown in FIG. 3A, the shoulder 28 is angled about the periphery of the lower drum 16 because of the helical scanning method used in the videotape machine (e.g., enters at high point and exits at low point). The shoulder 28 is also radially tapered so as force the tape towards the surfaces 12A and 16A of the upper and lower drums 12 and 16 thereby providing better contact with the heads 9. In some cases, sticktion may be encountered when the tape is moved across the upper drum 12. In order to reduce the sticktion, the upper drum 12 includes a pair of bumps 30 that extend past the outer peripheral surface 12A of the upper drum 12 as shown in FIG. 3B. The bumps 30 provide an air gap between the top edge of the backside of the tape 7 and the outer peripheral surface 12A of the upper drum 12 (the air gap helps to reduce sticktion between the tape and the upper drum).
Referring back to FIGS. 2A and 2B, the spindle assembly 20 includes a spindle 46 and a spindle pad 48. The spindle 46 is rotatably coupled to the upper base 22 via a set of bearings 52 and powered by a motor (not shown) housed within the lower base 24. The motor is typically configured to rotate the spindle 46 along an axis 54 at speeds up to 10,000 revolutions per minute (rpm). One end of the spindle pad 48 is attached to the spindle 46 while the opposite end is attached to the inner drum 14. The spindle pad 48 includes a guide post 33 and a mounting flange 50. As shown, the guide post 33 extends into a portion of the cavity 32, and the mounting flange 50 provides a mounting surface for securing the inner drum 14 thereto. Furthermore, the guide post 33 includes a guide hole 34 configured for supporting a slip ring assembly (not shown).
Unfortunately, the design and implementation of the drum assembly 10 leads to problems which may shorten part life and the proper functioning of the video tape machine in which it is used. For example, one problem associated with the above assembly is that the upper and lower drums 12 and 16 include polished aluminum outer peripheral surfaces 12A and 16A. The polished aluminum outer peripheral surfaces 12A and 16A, which contacts the tape 7, is not very effective at preventing sticktion problems, and it is soft material that is suceptable to wear. Referring to FIG. 3A, the shoulder 28 that guides the tape 7 around the drum assembly 10 may wear as the tape 7 is moved across its surface. The wear can lower the position of the shoulder 28 thus shifting the position of the tape 7 relative to the heads 9. This may make it difficult for the heads 9 to record or reproduce. The contact between the tape 7 and the outer peripheral surfaces 12A and 16A can also produce undesirable particles 60 (from both the shoulder and the tape). These particles may adhere to the backside or data side of the tape 7 thus causing signal dropout problems. The particles 60 may also build up on the shoulder 28 possibly shifting the position of the tape 7 relative to the heads 9 (e.g., pushing the tape away from the surface) or making it more difficult for the tape 7 to move along the shoulder 28. The taper in the shoulder 28 may further trap particles 60 on the shoulder 28, i.e., no place for the particles to go. All of these problems may make it difficult for the heads 9 to record or reproduce. Another problem associated with the drum assembly is that the drums are cold plated (e.g., chemical process that occurs at the molecular level) to help protect the surfaces of the drum. The cold plating process, however, distorts the shape of the drum. For example, the upper drum may be distorted into an egg shape (e.g., the diameter is not uniform). As should be appreciated, distortions such as these may make it difficult for the heads 9 to record or reproduce. Another problem associated with the drum assembly 10 is that the bumps 30 (as shown in FIG. 3B) tends to cause tape wear as for example shedding that produces undesirable particles 60. It may also make it difficult for the heads 9 to record or reproduce since its only located at the top edge of the tape 7 (e.g., produces a deformed signal such as spikes).
In view of the foregoing, there are desired improved methods and apparatuses for manufacturing and/or refurbishing a drum assembly used in a video tape machine such as the DVW, DNW, HDW models manufactured by Sony of Japan.